As requested by AFa340-300E i performed a search into the 767 landing gear issue. i have to admit what i read was interesting. but the answer is easer than all the answers given. the 757 and 767 were designed to meet two different modes of flight. 757 = "short range" 767 = "long range". when designing for these differnet modes of flight different things are important. range, fuel consumption, cargo capacity, etc. due to placement of the wing, needed cargo space, the desire to have the smallest wheel well as possible and the dedsire to keep the aircraft from tilting when its on the ground, boeing designed the landing gear to move forward on retraction on the 767. where on the 757 it moves aft. so think about it, if the gear needs to move forward the forward tires need to be down so when it is retracted the "boggies" will be inline with the fuselage. the same is true if the landing gear retracts aft (757). as a point of interest the 707 gear moves straight in to the wheel wells so it has no tilt.